In the days and weeks following the Kansas City Chiefs’ brutal 18-16 home playoff loss to the Pittsburgh Steelers in January 2017, Alex Smith looked in the mirror for ways to improve.

Smith, then the Chiefs’ starting quarterback, had been told after the season by coach Andy Reid that he’d get at least one more year to lead the Chiefs, even though the team would explore drafting a young quarterback (which it did). What was left unsaid — but was obvious to Smith — was that after four years in Kansas City, Year 5 would be put up or shut up time.

So with that in mind, he took his workouts to another level.

His wife tweeted a photo of Smith carrying a large rock underwater during a Hawaiian vacation, and when Smith — who was once voted the NFL’s best-looking quarterback in an unofficial Sports Illustrated poll in 2016 — returned for training camp that August, he checked in at 6-foot-4 and 212 pounds, looking as lean as he had in years.

Smith’s arm was also livelier, and that, combined with a newfound willingness to consistently throw long, propelled him to hold off first-round rookie quarterback Patrick Mahomes and go on for a career year in which he became the league’s best deep-ball passer, at least statistically, and made the Pro Bowl for the second straight year.

Now, some of Smith’s performance can be attributed to the genius of desperation, as players often respond to an on-field challenge (like the selection of a young player at the position you play). But what’s also true is that Smith felt as sharp as he had in years, mentally, and that his diet might be as big a reason for that as anything else.

“Like, I fast all the time — daily,” Smith told Yahoo Sports. “It’s such a counterintuitive thing because my whole life, I’ve been training to get bigger.

“Honestly, I’ve tried a lot of goofy stuff over the years — as you get older, you just try stuff. But there’s only one thing I feel like I’ve really endorsed and this is it. It’s great.”

Smith allows himself to eat only between noon and 8 p.m., an approach he became intrigued with months before the Pittsburgh loss, shortly after the Chiefs signed quarterback Nick Foles to be his backup for the 2016 season.

Smith says Foles is a big believer in fasting and drinking bulletproof coffee — which is coffee mixed with butter and oil — and soon, everybody in the Chiefs’ quarterbacks room was trying it.

“When you put fat — a derivative of coconut oil — and you blend it in your coffee, that oil helps kick you into ketosis faster, and you produce more ketones,” Smith explained.

Smith played around with Foles’ approach during the 2016 season, but devoted himself fully to fasting 16 hours a day that offseason and quickly saw results, as he says he maintained the same weight — 212 pounds — but saw his body fat percentage shrink from 10 percent at the time to 4, which is what he checked in at right at the outset of the Washington Redskins’ most recent training camp.

“Your liver stores glycogen for ‘X’ amount of time, and when that depletes and you don’t have any sugar or carbs to run off of, your body kicks into ketosis and pulls stored fat cells … so essentially, you’re using your own fat for energy,” Smith explained.

The science generally checks out. The concept of fasting has grown in popularity over the years, and several prominent doctors have written about the benefits of it, which range from increased weight loss to sharper mental clarity, with the latter being a byproduct that Smith — who had a few concussion scares in Kansas City — can attest to.

“I really liked the way I felt on it — focused and locked in, really locked in,” Smith said. “You’re getting these ketones in your body, and they’re really good for your brain. A lot of this is to fight dementia, fight Alzheimer’s, and your body is cleaning itself. When you’re not putting food down your mouth all day, your body has to process food and spend energy to process that, and when you stop giving it food, it can kind of go into self-repair mode.”

Since his offseason trade to the Redskins, Smith has continued his 16-hour fasts, even during training camp, when he’d wake up early, have water and coffee and practice, all before eating an ounce of food.

“It’s helped me focus these last few years … I feel really good practicing,” Smith said. “I feel light, my arm feels great, I feel like I have far less inflammation because of it. And I certainly leaned up quick.”

This practice has also helped Smith enjoy eating more. He eats very healthy via the usual fare — chicken, fish, proteins, good fats — but he doesn’t count calories, and he allows himself to cheat a bit.

So let’s just say, when noon hits at the Redskins’ practice facility, it’s on.

“Bro, you should see me each lunch and dinner — [I’m eating] five plates,” Smith said with a hearty laugh. “I’m crushing it. Killing it. Yesterday I had four plates of jambalaya, greens and this corn salad. I’m hungry, and I actually enjoy eating in my window. Like, I really do, I really look forward to eating.”

All the quarterbacks in the 2016 Chiefs’ quarterbacks room have tried fasting, including Foles and then-backup Tyler Bray, who is currently on the Chicago Bears’ practice squad.

Smith said Bray leaned up quite a bit in 2016 while adopting the fast, and the process apparently worked because Bray has done it intermittently since he got out from under Smith’s tutelage in Kansas City this offseason.

“Alex is obviously smart — he researches everything he ever does or puts in his body,” Bray said. “I don’t know how much it translates to football, but overall body health? I think it has some translation.

“But I don’t think if you’ll go out [and fast] and drink bulletproof coffee you’ll win the Super Bowl. I don’t think there’s a scientific translation to that.”

The latter statements were a nod to Foles, who won Super Bowl MVP in February and is described by both Bray and Smith as a major proponent of the approach.

“He’s dialed in with the bulletproof coffee now,” Smith said. “It’s his baby.”

Since Smith has brought the approach to Washington, he at least managed to intrigue a few of his teammates, including his backup, Colt McCoy, and the Redskins’ passing game coordinator, Kevin O’Connell.

As for himself, as you might imagine, Smith doesn’t plan on stopping his 16-hour fasts anytime soon.

“It’s something I do,” Smith said, “that I feel like has helped me.”

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